I'm only 20 minutes away from school,I have to rush.
Question:What does the first sentence mean?Does it mean that it's 20- minute walk or ride from school? Or does it mean that I just have 20 minutes left to go to school,because school begins in 20 minutes?

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I was unable to get out…

Since then, I have been afraid…

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'20 mintes from school' normally means that it takes 20 minutes to get to school, by whatever means of transportation you are talking about.  However, 'I have to rush' makes it sound like that have to be at school in 20 minutes.  They could be using the phrase in an unusual way.